Carrier telegraph circuits



Au 19, 1930. R -H CLAPP 1,773,092

CARRIER TELEGRAPH CIRCUITS Filed March 12. 1929 ||||||H||. V I mi MutralSounds:

. Stat/1m I gs lNVENTOR 3 BY 'i@@ ATTORN EY Patented Aug. 19, 1930UNHTED STATES PATENT OFFICE ROBERT E. cLArr, or RAMSEY, NEWJERsExnssIGNOR To AMERICAN TELEPHONE AND TELEGRAPH COMPANY, a COPORATION or NEW YORK CARRIER TELEGRAPH CIRCUITS Application filed March12, 1929. Serial No. 346,361.

This invention relates to carrier telegraph systems, and moreparticularly to carrier telegraph systems in which two-way half-duplexOperation is provided with the requirement of only one carrierfrequency. The principal Object of the'invention is to provide fortelegraph operation of the type indicated above Without the'requirementof line balance.

In accomplishing his purpose, the applicant employs the method ofOperation in accordance with which carrier current is sent .into theline to produce a spacing signal and is cut off for a marking signal,and so arranges the apparatus and circuit that the receiving apparatusat either end'of the tele graph circuit responds freely to currenttransmitted from the distant end i but is rendered incapable ofoperation while current is being'sent out from the near end.

The .invention will beclearly understood when. the following detaileddescription is read with reference to the accompanying drawing, whichshows diagrammatically, and

in part schematically, one desirable embodiment of the invention. In thedrawlng there is shown 1n such detail as is deemed advisable theapparatus and circuit arrangements of a station X at one end of acarrler'telegraph system. The

connection from station X to a subscribers office is indicated at theleft of the drawing, and a two-wlre line 1s shown connecting station Xto a distant station Y at the right, it being understood that theapparatus and circuits of station Y are identicalwiththose of station X.While the apparatus of a single carrier channel only is shown in thedrawing, it is understood that other similar channels may be provided ina multiplex system.

At station X a vacuum tube oscillator O is the source of carrierfrequency oscillations and is connected to the lnput of the vacuum tubeamplifier A which transmits the carrier current to the line. The polarrelays R and R the resistances 1' and T the sending key K, the neutraland polar sounders (schematically shown), the receiving relay R and thereceiving amplifier A and the rectifier through the armature, the tube Ais rendered opcrative,:and carrier current is sent over the line toproduce a spacing signal at station .Y.

Associated with thevacuum tubes A and D in the receiving channel is asecond rectifier tube D connected as shown, A transformer T has its lowwinding W bridged across the input of the rectifier tube D and its highwinding W connected in the plate circuit of rectifier tube D .There isimpresed on the grid of tube D 21; negative potential great enough toprevent the flow of current in the plate circuit of the tube whensignals are received from the distant station 1 Y. Due to this biasingvoltage, of course, and the resultant high impedance offered by thetransformer T, the bridging of the transformer windingw across the inputof tube D causes practicallynoloss therein, and the signaling fromstation Yfto station X is not interfered with. v

When, however, the carrier current from oscillator O is sent out, thiscurrent being approximately QOdb. higher than the current received overthe line from SttltlOIlqY, the negative voltage on the grid of tube Disreduced to the pointat which current flows in the plate circuit ofthat tube. This flow of current through winding W of transformerTreduces to a low value theimpedance of the-transformer seen from theinput circuit of tube 1),, and the effect'of-the bridged winding Wbecomes practically, that of a short circuit on the input of tubeDConsequently, any current transmitted through amplifier- A will notoperate the tube D and the receiving relay R is unafiected;

.l/Vhen thesending key K at station Xanda a hightreq the sending key atstation Y are both closed, there is no carrier current on the line, andthe receiving circuits at both stations are 1n condition for the recetion of signals. If,

5 now, the operator at for instance, opens his k K and carrier; currentfrom the oscillator tg is sent out-to produce a spacing signal at Y, thelarge transmitted current causes in efiect a short circuiting of theinput of the rectifier 1);"81jt1th6 receiving relay R 1s, of

course, not operated; at Y, however the signal is received in the usualway. when the operator at Y wishes to break in, he opens his sendingkgy, and carrier current from the oscillator at 18 sent into the line.As soon wthesemder at X closes the key K,thereceiving relay R, isoperated to its spacing contact 'S, which connects positive battery tothat armature. Withthis condition, no curwent flows in thesending loopthrough the resiatanee R because the ends of that circuit cnn'noct toequal potentials. Also,the current is reversed in the windings which areconthrough tht t esistance r to ground, 95 thus hoIdin the relayinmarking condition aabefore. inoenopurrentflows in the subscrsiber'sloop,operation of his key has no ef- *feet; and the control ofthe circuit haspassed ttt theoperator'at station Y. Thus it is seen so that thearrangementdisclosed meets the requirements of'hal f du lex operation.

@ 1 v ampi fier tube A serves to the shunt ng efiect resultin from theionof tube D, from inter ering with as t? current transmitted to theline from oscildator 0. The sending amplifier tube A serves tostabilize? the impedance which terminates the oscililator clrcuit.

' While the invention has been disclosed in soj-onespecificembodimenttor the purpose of "illustration, itis-tebe understood that itis of embodiment-in other and difierent forms within the true scope ofthe invention Aasdeilnedin the dedclaims. is claims he carrier telegraphcircuit, a sending *channel and a-recai ng channel in association with atransmission line, means assosaid sending channel for sending uencywavesthercover, receiving apperat usm said receiving channel, and arectifier responsive to hi h frequency waves fiipting'in said sen' ingchannel for dis- *saidreceiving apparatus.

w a carrier telegraph circuit, a sending chl,nnel and a receivingchannel in association with a transmission line, an oscillator associated' with said sending channel, a rereetifier and a relay controlledthere'- may "in said receiving channel, and an auxthreeplecjtrode vacuumtube rectifier ted' with said receiving channel and its platecircuit'connected to form in effect a shuntimpedauee across the input ofreceiving rectifier, said auxiliary rectifier being biased so that platecurrent flows therein only when waves which originate in said oscillatorflow in the circuit.

3. In a carrier telegraph circuit, a sending channel and a receivingchannel in association with a transmission line, an oscillatorassociated with said sending channel, a sending relay controlling saidsending channel to send out or cut off the waves originating in saidoscillator, a receiving rectifier and-a receiving relay controlledthereby in said receiving channel, and an auxiliary three-electrodevacuum tube rectifier associated with said receiving channel and havingits plate circuit bridged across the input of said receiving rectifierthrough a transformer, said auxiliary rectifier having its grid biasedto prevent 'a flow of plate current in said rec tifier except when waveswhich originate in said oscillator are sent into the circuit.

4. In a carrier telegraph circuit, a sending channel and a receivingchannel in association with a line, a source of carrier waves associatedwith said sending channel, a receiving rectifier and a relay co ntrolledthereby in said receiving channel, and an auxiliary three'elcctrodevacuum tube rectifier associated with the input of saidreceivingrectifier in such a manner that when no current flows in theplate circuit of said auxiliary rectifier no appreciable loss isintroduced in said input, but when current flows in said plate circuitsaid input is in effect short-circuited, said auxiliary rectifier beingbiased so that normally no current flows in its plate circuit, but whena carrier wave is sent into the circuit from said oscillator, currentflows in said plate circuit. 7

5. In a carrier telegraph circuit including a sending channel and areceiving channel in association with a transmission line, a source ofcarrier waves associated with said sending channel, a rectifier in saidreceiving channel and a receiving relay controlled thereby,

the method of accomplishing two-way transmission on a single carrierfrequency which consists in bridging an Impedance across the input ofthe rectifier, adjusting said imped ance to introduce normally noappreciable loss 'in-said input, and causing a carrier wave from thesource associated with the sending channel to reduce said impedance tointroduce a loss in said input sufficient to prevent operation of therectifier.

In testimony "whereof, I have signed my name to this specification this11th day of March, 1929. V

. ROBERT H. CLAPP.

